Method and apparatus for comminuting suspensions of solid material



Feb. 18, 1958 J. o. SCHERER 2,823,868

METHOD AND APPARATUS FOR COMMINUTING SUSPENSIONS OF SOLID MATERIAL Filed Dec. 6, 1954 Suspension Refined, Gas-free Suspension Fig, i 58 1110; lurlllam mmrllla IIME ohn O. Jcbcrer' j 35 INVENTOR.

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United States Patent METHOD AND APPARATUS FOR COMIVIINUTING SUSPENSIONS OF SOLID MATERIAL John O. Scherer, Grosse Pointe, Mich., assignor to R. P. Scherer Corporation, Detroit, Mich., a corporation of Michigan Application December 6, 1954, Serial No. 473,263

12 Claims. (Cl. 241-2) .The present invention relates to an apparatus and method for comminuting solids in a suspension under vacuum. his highly desirable to preparesuspensions or slurries of finely divided solids which contain no air or entrapped gases. Normally, this is done by passing the material. through a hammer mill or the like and subsequently evacuating the fine suspension. By comminuting under vacuum in accordance with this invention an especially fine suspension is produced because the absence .of air not only eliminates bubbles, but greatly improves wetting of the solid particles by eliminating the air film around the particle which prevents wetting. Furthermore, the introduction of the suspension at atmospheric pressure into the comminuting apparatus, which is maintained at reduced, pressure causes the air or other gas included in the solid particles or agglomerates to burst or explosively disintegrate the particles as the air rapidly expands.

One of the difl'iculties presented in designing a comminuting apparatus for operation under vacuum involves connecting the shaft of the comminuting or hammer mill to a power source. The shaft rotates at terrific speeds and is of relatively large diameter to take the loads in volved. Both factors make it diflicult to retain the seal Where shaft enters mill chamber.

A primary object of my invention is toprovide an improved method and a simple and reliable apparatus for efficiently comminuting suspensions of solids to produce a substantially air-free finely divided product.

Another object of my invention is to provide a comminuting apparatus capable of operating under a vacuum or partial vacuum, so constructed that the air or gases released by the material being treated, as Well as accidentally inward-leaking air, are free to flow through specially provided passages from one compartment of the apparatus to another without influencing the flow of material being treated.

.Another object of my invention is to provide an efficient,

practical comminuting apparatus that will operate continuously at sub-atmospheric pressure and which requires no pressure-sealing device to seal the power transmitting .shaft at its point of entry into the milling chamber.

These and other objects will become apparent from the followingdescription when read in conjunction with the accompanying drawing, in which:

Figure 1 is an elevational view, partly in section, .of the apparatus of my invention, and

Figure 2 is a similar view showing a modificationin the motor for driving the mill.

The comminuting apparatus shown in the drawing'may be mounted on the hinged lid 12 of a large receiving vessel adapted to receive the suspensionproduced in the comminuter. The lid 12 is. sealed againstagasket 8.10- cated between the rim 13 of the cover and the upper edge 15 of the receiving vessel. The comminuter or mill is of conventional hammer mill construction having a plurality of spaced blades 21 mounted on a central shaft "within the housing 23. An outlet opening in the base of therriill housing provides a passage for the suspension discharged through the arcuate screen 29 of the mill .to the receiving vessel 10. For construction details of the mill,l reference is made to Patent No. 2,417,184 to Wagner et a The motor 52 for driving the comminuter has a shaft 54 mounted on bearings 5? and 56. A cantilever extension 22 projects from the end of shaft 54 through the intermediate chamber 72 and felt oil seal 28 in the rear wall of the mill housing into said mill housing wherein it mounts the mill head 25. On shaft 22 between will head 25 and rear housing well 26 is affixed a flinger ring 24 which, together with soft felt seal 28, serves to minimize the seepage of process material into intermediate chamber 72.

Within the intermediate chamber 72 there is mounted on shaft extension 22 a second flinger ring 66 serving as a stop toprevent seepage of material along the shaft into bearing 56. Flinger ring 66 is provided with a dished rim 68 of sufficient axial depth to extend over and beyond the face 69 of bearing support 67, which in turn is provided with a radially extending flange 76.

into the receiving vessel 10. This passage 74 will, be-

causeof its location, also serve as a drain for possible seepage.

The interior of motor housing 56 is in gaseous communication with intermediate chamber 72 through tube 76 passing through motor end plate 5555 at the lowest interior point of the motor housing 5t) but above the lowest point of the intermediate chamber '72. Tube 76 further extends a short distance into intermediate chamber 72, as indicated, to prevent seepage into the motor housing while the device is tilted up.

Intermediate chamber 72 at its lowest point connects via tube 74 with the interior of receiver if The result of this arrangement is that so long as vent valve 55 in the end of motor housing 50 is closed, the gas pressure inside motor housing 5% and intermediate chamber 72 will.be the same as the pressure prevailing in the receiver .10. Opening vent valve 55 while receiver 10 is at subatmospheric pressure will cause air to rush into motor housing 50, sweep through passage 76 into intermediate chamber 72 and on through tube '74 into receiver 10, scavenging the various chambers and passages as it goes.

The interior of mill housing 2% besides being in communication with receiver 10 through the discharge screen 29 and discharge opening 35 is further in gaseous communication with receiver 10 via the connection 38 relatively centrally located on the front cover 23 of the mill, via tube 36.

It is apparent then, that when supply valve 31 and vent valve 55 are closed and air is removed from receiver 10 via connection 14 to a vacuum pump, air will fiow from all the enclosed chambers of the machine to the receiver and veryshortly after the desired sub-atmospheric pressure is reached in receiver it), the pressures in all the other chambers will balance off atthis same pressure and there will be no pressure differentials existing between the various chambers.

Conduit 32 connects to the interior of the mill housing through the opening 33, and serves to conduct the suspension to be comminuted from the supply reservoir (notshown) "tothe'niill. A valve 31' in the line 321s V ner;

employed to control the flow of the suspension to the mill. pension supply reservoir and supply valve 31 opened, atmospheric pressure will cause the suspension to flow into the. mill'jwhere itwill be acted upon inthe desired man- The' air or gas entrained or dissolved will be released primarily in the mill chamber by the action of the hammers and, consequently, the gas pressure in the mill housing will tend to rise above that in the other chambers. Tube 36 and connection 38, however, provide an escape path for this gas to receiver and so to the vacuum pump with the result that the actual pressure difference existing between the mill housing and the receiver is negligible and of insuflicient magnitude to cause appreciable seepage through the felt oil seal 28 or to tend to force throughout material through mill screen 29. Y e I The rather elaborate system of fiinger rings and shields in the intermediate chamber is incident to the fact that the whole apparatus'is to be tilted'up through an angle of approximately 90 for convenient removal or replacement of the receiver 10 as well-as for convenient cleaning of the apparatus, and when in this position the natural flow path for any 'materialwhich may have passed felt seal 28 would be towardbearing 56, which would be damaged if contaminated by the material being treated.

The motor housing 54 comprises a jacket through which cooling liquid is circulated through lines 64 and 62 in the direction indicated in the drawing. The cooling liquid conducts away the heat generated by the comhousing 50, intermediate chamber 72, and comminutor 20 all communicate with the vessel 10, which is connected to a source of vacuum through pipe 14 in the top 12 of the vessel. By providing communicating passages assumes With the end of conduit 32 immersed in the susin this manner the vacuum drawn on the vessel 10 will prevail within the comminutor, the intermediate chamber, and the motor housing so that'no pressure diiferential exists between these chambers; The pressure equalizing tube 36 between-the mill chamber'and receiving vessel 10 is particularly important as without it the air or gas which is released mainly in the mill chamber would have to fiow to the receiver vessel 10 through the screen 29, which when covered with the material in process offers an appreciable resistance to the passage of air or gas. On the other hand, because tube 36 connects quite centrally. to mill chamber, very little throughput material willpass through tube as into receiver 10.

In operation, the interior of the comminutor is evacuatedtthmughzthe communicating conduit 36 between the housing23 aiidithe receiving vessel 10 by'means of a vacuum pump 'connectedto line 14. The suspension or slurry containing larger particles, lumps, or agglomerated particles of solid material to be finely subdivided is .then drawn into the comminutor 20 through the supply :ceiving vessel, maintained under the same degree of vac- -.uum as the comminutor. The particles in the suspension are not only disintegrated due to violent agitation by the swiftly moving blades 21, but additionally, introduction of the particles into'the comminutor housing at reduced pressure causes the air within the particles to rapidly expand, which aids in breaking up the particles or agglomerates into smaller sized particles. The finely divided solid suspension, which may be of colloidal size, passes through the screen 29 in the bottom of the comminutor 4 v t and falls through the opening 30 into the receiving vessel10. Y

The amount of vacuum to be maintained within the comminuting device is dependent upon the volatility of the particular material being treated. Generally, I prefer to operate at a vacuum of 29 to 29 /2 inches of mercury. If the materials are more highly volatile or sublime readily, the absolute pressure willhaveto be increased accordingly. It is important, of course, that no excessive amount of evaporation or sublimation occur during the comminuting process.

One of the foremost advantages of this invention is that the final product needs no further treatment to render it air free. By carrying out the subdivision of the solid particles in vacuum, the subdividing operation is not only facilitated, but dissolved or suspended air is removed from the suspension and no air is whipped into the suspension as is the case where the comminutor is operated at atmospheric pressure. Previously, it was neccssary to treat the finely divided suspension after comminuting by a separate evacuation process to remove the air that had been whipped into the material during'cornminuting. r

ln'Figure 2 I have shown a modification of the invention in which only the motor is constructed differently. Instead of enclosing the entire motor as shown in Figure 1, only the rotor 90, the shaft 54 and the bearings 56 and 57 are enclosed. This is accomplished by mounting a sleeve 91 of non-magnetic material between the rotor and the stator 92 of the motor 52 to provide a gastight housing 94. This permits the stator to be exposed to the atmosphere for cooling purposes. Since only the rotor is sealed within the housing 94, it is not necessary to provide a cooling'jacket; The'mo'tor'will' 'perform satisfactorily 'withonly the rotor confined. To provide gaseous communication-between the housing 94 and the sealed intermediate chamber 72,"an aperture 95 is provided in the rear wall 58 of said'chamber. This aperture corresponds to the opening 76 in Figure l, and accomplishes the same purpose; w

While I have shown and described specific embodiments of the present invention, it will, of course, be understood that various mo'difications and alternative constructions may be made without departing from the true spirit and scope thereof. It is my intention, therefore, by the appended claims to cover all modifications falling within their true spirit and scope.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In an apparatus for continuously comminuting a suspension of solid material under a vacuum, comminuting mill having an'inlet and an outlet opening, a receiving vessel communicating with said outlet opening connected to a source of vacuum, and a pressure equalizing line between the mill and the receiving vessel, and a shaft for driving the rotor of said mill, said shaft being enclosed in a chamber communicating with said receiving vesseL 2. In an apparatus for continuously comminuting a suspension of solid material under a vacuum, a comminuting millhaving an inlet and an outlet opening, a receiving vessel communicating with said outlet opening and connected to a source of vacuum, a pressure equalizing line between the mill and the receiving vessel, and a motor for driving the rotor of said mill, said motor being enclosed in a sealed housing also communicating with said receiving vessel. e I

3. In-an apparatus for continuously comminuting a suspension of solid material under a vacuum, a comminuting mill having an inlet and an outlet opening, a receiving vessel communicating with said outlet opening and connected to a source of vacuum, a pressure equalizing line between the mill and the receiving vessel, 21

I motor for driving the rotor of said mill, said motor being enclosed in a sealed housing also communicating with said receiving vessel, and an intermediate chamber between said motor housing and said mill, said chamber communicating with said receiving vessel.

4. In an apparatus for continuously comminuting a suspension of solid material under a vacuum, a comminuting mill having an inlet and an outlet opening, a receiving vessel communicating with said outlet opening and connected to a source of vacuum, a pressure equalizing line between the mill and the receiving vessel, a motor for driving the rotor of said mill, said motor being enclosed in a cooled gas-tight housing also communicating with said receiving vessel, and an intermediate chamber between said motor housing and said mill enclosing a shaft coupling said motor to said rotor, said chamber communicating with said receiving vessel and said motor housing.

5. The apparatus of claim 4 in which said enclosed shaft carries a flinger disc rigidly fixed thereto to prevent any of said suspension escaping around the shaft of the mill from flowing to the bearing of said motor.

6. In an apparatus for continuously comminuting a suspension of solid material under a vacuum, a comminuting mill having an inlet and an outlet opening, a receiving vessel communicating with said outlet opening and connected to a source of vacuum, a pressure equalizing line between the mill and the receiving vessel, a motor for driving the rotor of said mill, said motor being enclosed in a cooled gas-tight housing, an intermediate chamber between said motor housing and said mill enclosing a shaft coupling said motor to said rotor, said chamber being in gaseous communication with said receiving vessel and said motor housing, a bearing for said shaft mounted within a common wall between said motor housing and said chamber, a collar secured to said wall and surrounding said bearing, and a flinger disc of larger diameter than said collar rigidly fixed to said shaft to prevent any of said suspension escaping around the shaft of the mill from flowing to the bearing of said motor.

7. In an apparatus for continuously comminuting a suspension of solid material under a vacuum, a comminuting mill having an inlet and an outlet opening, a receiving vessel communicating with said outlet opening and connected to a source of vacuum, a pressure equalizing line between the mill and the receiving vessel, a motor for driving the rotor of said mill, said motor being enclosed in a sealed housing, an intermediate chamber between said motor housing and said communicating mill, said intermediate chamber communicating with said motor housing and said receiving vessel.

8. The apparatus of claim 7 in which a vent valve is provided to permit communication of said motor housing with the atmosphere.

9. A method for comminuting solids in liquid suspension which comprises introducing said suspension into an enclosed comminuting mill maintained at a reduced pressure of about 29 inches of mercury to cause disintegration of the solid particles by explosive escape of air trapped within the particles and by violent agitation due to a high rotative speed of the mill, and discharging the air-free finely divided product suspension into a receiving vessel maintained at substantially the same pressure as the comminuting mill.

10. In an apparatus for continuously comminuting a suspension of solid material under a vacuum, a comminuting mill having comminuting blades, an inlet and an outlet opening, a receiving vessel communicating with said outlet opening and connected to a source of vacuum, a pressure equalizing line between the mill and the receiving vessel, and a motor for driving the mill blades, said motor having its rotor enclosed in a gas-tight housing made of non-magnetic material, and said housing being in gaseous communication with said receiving vessel.

11. In an apparatus for continuously comminuting a suspension of solid material under a vacuum, a comminuting mill having comminuting blades, an inlet and an outlet opening, a receiving vessel communicating with said outlet opening and connected to a source of vacuum, a pressure equalizing line between the mill and the re ceiving vessel, a motor for driving the mill blades, said motor having its rotor enclosed in a gas-tight housing made of nonmagnetic material, and said housing being in gaseous communication with said receiving vessel, an intermediate chamber between said gas-tight housing and said mill enclosing a shaft coupling said motor to said mill blades, said chamber communicating with said gastight housing and said receiving vessel.

12. The apparatus of claim 11 in which a vent valve is provided to permit communication of said gastight housing with the atmosphere.

References Cited in the file of this patent UNITED STATES PATENTS 64,834 Bruce May 21, 1867 744,810 Sherman Nov. 24, 1903 1,575,717 Plauson Mar. 9, 1926 2,153,537 Heath Apr. 11, 1939 2,417,184 Wagner Mar. 11, 1947 FOREIGN PATENTS 845,192 Germany July 28, 1952 

